Lubricant supply system for an engine

ABSTRACT

A lubricant supply system for an engine includes an oil pump activated by an engine having a crank system and a valve system, a main passage connected to the oil pump for supplying a lubricant to the engine, a crank system passage branched from the main passage for supplying the lubricant to the crank system, a valve system passage branched from the main passage for supplying the lubricant to the valve system, an oil pressure relief valve disposed in the crank system passage, and an oil pressure detecting type orifice valve disposed in the valve system passage.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims priority under 35 U.S.C. 119 with respect to a Japanese Patent Application 2002-085949, filed on Mar. 26, 2002, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention generally relates to a lubricant supply system for an engine. More particularly, this invention pertains to a lubricant supply system for supplying lubricant discharged from an oil pump activated in response to rotation of a crank shaft to an engine. The engine includes a crank system and a valve system. The crank system is supplied with the lubricant from the oil pump via a main supply passage and a crank system supply passage branched from the main supply passage. The valve system is supplied with the lubricant from the oil pump via the main supply passage and a valve system supply passage branched from the main supply passage.

BACKGROUND OF THE INVENTION

[0003] A conventional lubricant supply system for an engine has been disclosed in a Japanese Patent Laid-Open published as No. 06(1994)-212932. According to this disclosed lubricant supply system for the engine, a crank system lubricant supply passage, which is branched from a lubricant discharging passage communicating with an oil pump, is provided with a crank system orifice (a variable orifice valve) capable of reducing passage resistance in response to increase of an engine RPM that stands for engine revolution per minutes. A valve system lubricant supply passage, which is also branched from the lubricant discharging passage, is provided with a valve system orifice (a variable orifice valve) capable of increasing passage resistance in response to the increase of the engine RPM.

[0004] According to another conventional lubricant supply system for an engine, a lubricant discharging passage is branched to a crank system lubricant supply passage and a valve system lubricant supply passage. The valve system lubricant supply passage is provided with a variable orifice valve operated in response to a detected oil pressure so as to supply the lubricant at a constant pressure level to the valve system whenever an oil pump is activated.

[0005] Further, another conventional lubricant supply system for an engine includes a variable displacement type oil pump connected to the engine and a variable orifice valve. The amount of lubricant discharged to the engine body is controlled by the variable displacement type oil pump and the variable orifice valve in response to a lubricant temperature.

[0006] As described above, the lubricant can be properly supplied to the engine at an adjusted amount and the oil pump can be activated with an improved efficiency, thereby capable of effectively improving fuel consumption of the engine.

[0007] According to the lubricant supply system disclosed in the Japanese Patent Laid-open published as No. 06(1994)-212932, the oil pressure discharged from the oil pump can be restrained corresponding to operation of the crank system orifice and the valve system orifice. The disclosed lubricant supply system employs a fixed displacement type oil pump, thereby the amount of the lubricant discharged from the oil pump can be serially increased in response to increase of an engine RPM. Accordingly, the amount of lubricant discharged from the oil pump can be restrained comparing with the amount of lubricant discharged from a conventional oil pump during the crank shaft of the engine being rotated at a low speed, thereby the fixed displacement type oil pump can be activated with an improved efficiency. However, the oil pressure supplied to the crank system can be substantially equal to or greater than the oil pressure required by the crank system, thereby excessive lubricant may be supplied to the crank system. The fixed displacement type oil pump can be replaced by a variable displacement type oil pump. However, driving power loss of the oil pump may not be able to be reduced down to a sufficient level.

[0008] According to the above described lubricant supply system having the variable displacement type oil pump and the variable orifice valve, a lubricant discharging passage connected to the oil pump is controlled to have a smaller diameter by the variable orifice valve when the lubricant temperature is relatively low, thereby reducing an amount of the lubricant discharged from the oil pump. Meantime, torque activating the oil pump is increased in proportional to an oil pressure discharged from the oil pump. Further, a relief pressure of the oil pump is generally determined based upon an oil pressure necessarily supplied to the crank system when the lubricant temperature is relatively high and the crank shaft of the engine is rotated at a relatively high speed. Accordingly, even if the lubricant amount at a downstream of the lubricant supply passage relative to the variable orifice valve is reduced by the variable orifice valve when the lubricant temperature is relatively low, the oil pressure at an upstream of the lubricant supply passage relative to the variable orifice valve, which is discharged from the oil pump, may be increased. In such a case, the torque activating the oil pump may not be effectively reduced.

[0009] Further, an oil temperature detecting type orifice valve is operated in response to the detected oil temperature and determines the amount of lubricant to be supplied to the engine. Therefore, excess oil pressure may not be easily reduced when the lubricant temperature is relatively middle or high and the crank shaft of the engine is rotated at a relatively high speed. Further, thermo wax or shape memory effect alloy (SMEA) is employed for the variable orifice valve, thereby the manufacturing cost thereof will be high.

[0010] The present invention therefore seeks to provide an improved lubricant supply system for an engine capable of supplying the lubricant at an optimal amount without employing highly-cost variable orifice valve.

SUMMARY OF THE INVENTION

[0011] According to an aspect of the present invention, a lubricant supply system for an engine includes an oil pump activated by an engine having a crank system and a valve system, a main passage connected to the oil pump for supplying a lubricant to the engine, a crank system passage branched from the main passage for supplying the lubricant to the crank system, a valve system passage branched from the main passage for supplying the lubricant to the valve system, an oil pressure relief valve disposed in the crank system passage, and an oil pressure detecting type orifice valve disposed in the valve system passage.

[0012] According to another aspect of the present invention, the oil pressure relief valve reduces an oil pressure in the crank system passage to be less than a predetermined oil pressure when the oil pressure in the crank system passage becomes substantially equal to or greater than the predetermined oil pressure.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0013] The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures wherein:

[0014]FIG. 1 is a block view schematically illustrating an oil pressure circuit of a lubricant supply system for an engine according to an embodiment of the present invention;

[0015]FIG. 2 is a diagram illustrating a relationship between an engine RPM and an oil pressure of lubricant discharged from the oil pump to a main passage of the lubricant supply system for an engine illustrated in FIG. 1;

[0016]FIG. 3 is a cross-sectional view illustrating an example of an oil pressure relief valve illustrated in FIG. 1; and

[0017]FIG. 4 is a cross-sectional view illustrating another example of the oil pressure relief valve illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The invention will specifically described in connection with its embodiment. Here will be described one example of a lubricant supply system for an engine, to which the invention is directed. As illustrated in FIG. 1, lubricant stored in an oil pan 2 is sucked by an oil pump 1 activated in response to rotation of a crank shaft (not shown) of an engine E and is then discharged to a main passage P1. The main passage P1 branches to a crank system passage P2 and a valve system passage P3. The lubricant discharged from the main passage P1 is supplied to a crank system A of the engine E via the crank system passage P2 and to a valve system B of the engine E via the valve system passage P3. The lubricant supplied to the crank system A and the valve system B subsequently circulates to the oil pan 2.

[0019] As illustrated in FIG. 1, an oil filter 3 is disposed in the main passage P1 communicating with a lubricant supply outlet of the oil pump 1 so as to eliminate foreign substances from the lubricant. A regulating valve 1 a is disposed in parallel with the oil pump 1. The regulating valve 1 a regulates the maximum oil pressure of the lubricant discharged from the oil pump 1 at a certain oil pressure level. The lubricant is returned to the oil pan 2 by the regulating valve 1 a when the actual oil pressure discharged from the oil pump 1 becomes substantially equal to or greater than the certain oil pressure level.

[0020] An oil pressure detecting type orifice valve 7 disposed in the valve system passage P3 functions for increasing passage resistance by narrowing the passage in response to increase of an inner pressure applied to the valve system passage P3 by the lubricant flowing therein. The amount of the lubricant discharged from the oil pump 1 is increased in response to increase of the engine RPM, thereby the inner pressure applied to the valve system passage P3 is increased. In such a case, the orifice valve 7 functions for effectively restraining the lubricant from being excessively supplied to the valve system B.

[0021] As illustrated in FIG. 2, the oil pressure discharged from the oil pump 1 varies depending on the engine RPM in accordance with the lubricant temperature. Generally speaking, the oil pressure required by the crank system A is determined based upon the oil pressure required at a relatively high lubricant temperature so as to prevent seizure during the engine rotating at a relatively high speed. An oil pressure relief valve 6 (illustrated in FIG. 1) is disposed in the crank system passage P2. The oil pressure relief valve 6 hereby drains the lubricant to the oil pan 2 when the oil pressure being supplied to the crank system A becomes greater than the oil pressure required by the crank system A. It is further preferable that the maximum oil pressure of the lubricant discharged from the oil pump 1 is designed to possess a minimum ability for supplying the oil pressure required by the crank system A thereto.

[0022] Next, the description will be given for explaining the relationship between the engine RPM and the oil pressure discharged from the oil pump 1 with reference to FIG. 2. The oil pressure discharged from the oil pump 1 varies depending on the oil temperature even when the engine RPM are the same. According to a conventional lubricant supply system, the lubricant is supplied at an excessively high pressure when the crank shaft of the engine E is rotated at a relatively high speed. According to the embodiment of the present invention, the oil pressure relief valve 6 disposed in the crank system passage P2 controls the oil pressure discharged from the oil pump 1 at a constant pressure level within a range in which the engine RPM is equal to or greater than a predetermined engine RPM. Accordingly, the oil pump 1 can be effectively controlled to discharge an optimal oil pressure in response to the engine RPM as illustrated by a heavy line shown in FIG. 2.

[0023] An oil pressure relief valve (an oil pressure detecting means) illustrated in FIGS. 3 and 4 represents an oil pressure relief valve according to the embodiment of the present invention.

[0024] The oil pressure relief valve illustrated in FIG. 3 is employed as the oil pressure relief valve 6 according to the embodiment of the present invention when an oil pressure in the crank system passage P2 is prescribed. The oil pressure relief valve 6 illustrated in FIG. 3 is provided with a pressure receiving portion 16 for receiving the oil pressure in the crank system passage P2, an oil pressure shut-off valve 26 possessing an approximately conical structure, and an oil pressure relief spring 36. The oil pressure relief spring 36 is designed to determine a predetermined oil pressure to be drained to the oil pan 2. The pressure receiving portion 16 and the oil pressure shut-off valve 26 are assembled being biased in a left-hand side in FIG. 3 by a biasing force of the oil pressure relief spring 36. When the oil pressure in the crank system passage P2 becomes substantially equal to or greater than the predetermined oil pressure, the oil pressure relief spring 36 is compressed in a right-hand side in FIG. 3 and the oil pressure shut-off valve 26 is moved in the same direction, wherein the lubricant drained via the oil pressure shut-off valve 26 is circulated to the oil pan 2 via a guide portion of the oil pressure relief spring 36.

[0025] The oil pressure relief valve 6 illustrated in FIG. 4 possesses substantially the same basic structure as the oil pressure relief valve illustrated in FIG. 3. The set load of the oil pressure relief valve 6 illustrated in FIG. 3 is not variable, and yet the set load of the oil pressure relief valve 6 illustrated in FIG. 4 can be adjusted to be an optimal load by means of a screw. Therefore, the oil pressure relief valve 6 illustrated in FIG. 4 can determine the oil pressure for draining the lubricant to the oil pan 2 at an arbitrary pressure value. For example, the oil pressure for draining the lubricant to the oil pan 2 can be adjusted to be a relatively high pressure level when a set stroke of the oil pressure relief spring 36 is shortened by the screw. On the other hand, the oil pressure for draining the lubricant to the oil pan 2 can be adjusted to be a relatively low pressure level when the set stroke of the oil pressure relief spring 36 is elongated by the screw. The oil pressure relief valve 6 according to the embodiment of the present invention is not limited to the above-describe structure. The oil pressure relief valve 6 can possess a different structure as far as the oil pressure relief valve 6 functions in the same manner.

[0026] The conventional lubricant supply system properly and finely controls the amount of lubricant to be supplied to the engine body by use of the oil pump and the variable orifice valve. The lubricant supply system according to the present invention is provided with the oil pressure relief valve 6 disposed in the crank system passage P2 and the oil pressure detecting type orifice valve 7 disposed in the valve system passage P3, thereby the optimal oil pressure can be supplied to the passages P2 and P3. Therefore, the oil pressure discharged from the oil pump 1 can be maintained at a constant oil pressure level when the engine RPM is substantially equal to or greater than the predetermined engine RPM. Therefore, the excess oil pressure discharged from the oil pump 1 can be reduced while the crank shaft of the engine E has been rotated regardless of the lubricant temperature. Load applied to the oil pump 1 can be hereby reduced so that the torque activating the oil pump 1 can be effectively utilized, thereby capable of downsizing the oil pump 1. Further, the lubricant supply system according to the present invention is not required to possess a variable orifice valve with thermo wax or shape memory effect alloy (SMEA), thereby the manufacturing cost thereof can be reduced.

[0027] The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein is to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby. 

What we claim is:
 1. A lubricant supply system for an engine comprising: an oil pump activated by an engine having a crank system and a valve system; a main passage connected to the oil pump for supplying a lubricant to the engine; a crank system passage branched from the main passage for supplying the lubricant to the crank system; a valve system passage branched from the main passage for supplying the lubricant to the valve system; an oil pressure relief valve disposed in the crank system passage; and an oil pressure detecting type orifice valve disposed in the valve system passage.
 2. A lubricant supply system for an engine according to claim 1, wherein the oil pressure relief valve reduces an oil pressure in the crank system passage to be less than a predetermined oil pressure when the oil pressure in the crank system passage becomes substantially equal to or greater than the predetermined oil pressure.
 3. A lubricant supply system for an engine according to claim 2, wherein the predetermined oil pressure is preset to be greater than an oil pressure required by the crank system.
 4. A lubricant supply system for an engine according to claim 3, wherein the oil pressure detecting type orifice valve increases passage resistance of the valve system passage in response to increase of an inner pressure of the valve system passage, wherein the lubricant is restrained from being excessively supplied to the valve system.
 5. A lubricant supply system for an engine according to claim 2, wherein the oil pressure relief valve is an oil pressure detecting means.
 6. A lubricant supply system for an engine according to claim 5, wherein the oil pressure detecting means includes an oil pressure receiving portion, an oil pressure shut-off valve, and an oil pressure relief spring, and the oil pressure relief spring is compressed when the oil pressure in the crank system passage becomes substantially equal to or greater than the predetermined oil pressure.
 7. A lubricant supply system for an engine according to claim 6, wherein a set load of the oil pressure relief spring is a constant value.
 8. A lubricant supply system for an engine according to claim 6, wherein a set load of the oil pressure relief spring is a variable value. 